This study numerically investigates the effect of injector configuration on flow characteristics and performance of annular and cylindrical rotating detonation engine (RDE) combustors. For each type of the RDE combustor, stoichiometric hydrogen-air premixed gas was injected from the bottom (“base injection”) or from the side wall (“side injection”). In the side injection cases, thin vertical waves and high-pressure regions near the injectors were observed for both combustor geometries. Such pressure fields differ from the pressure fields observed in the combustors with bottom injectors. However, in all cases, more than 80% of the fuel was consumed, and the burned gas was accelerated to the speed of sound toward the outlet. In the side injection case, the ratio of the specific impulse to the theoretical value was about 98.3% for the annular combustor and 95.4% for the cylindrical combustor. The effect of injection configuration on the propulsive performance was not significant. Thus, it is concluded that RDEs with injectors on the combustor side wall can perform similarly to those with injectors on the bottom despite the different wave structures.

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Advanced closed-loop control of thrust and mixture ratio of hybrid rockets can be realized by combing a fuel mass flow rate control technique with a real-time fuel regression measurement. One of the promising techniques to realize real-time fuel regression measurement is the multi-material-additive-manufactured solid fuel with an integrated sensor probe structure. In this work, the destruction process of its regression sensor structure was visualized by the high-speed video from the top view of the sensor structure. The acquired high-speed video revealed the destruction process and its relationship with the time history of the voltage on the sensor structure. One of the findings is that unevenness or bumps of the rung form hot spots with strong emission, leading to the dropping-off and entrainment of the fragmented rung into the diffusion flame. Another important finding is that the destruction process of the rung starts before the rapid voltage increase, but it precedes the more intensive and frequent destruction. The post-processing of the sequential frames of the high-speed video successfully provided the observation of the fuel surface behind the diffusion flames. These reconstructed videos visualized the motions of the fragmented rung remaining on the fuel surface. The physical destruction process of the regression sensor structure revealed in this study can contribute to the improvement of the sensor structure design to avoid the unexpected off-nominal responses previously observed.

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